Thermally forced winds that blow up or down the sidewall slopes in a mountain valley, and the accompanying countercurrents when present; the slope-wind components of the mountain–valley wind system. During the daytime this system consists of upslope (anabatic) flow adjacent to the slope and often a compensatory return current directed downslope just above the upslope layer. At night it is a downslope (katabatic) flow layer near the slope, sometimes with a return flow aloft.